This invention relates to an electronic balance provided with a built-in weight calibration of the balance.
Generally, in known electronic balances calibration is conducted by loading the weighing means including a load sensor with a weight of a known mass approximating that of an object to be measured, and changing or otherwise adjusting the calibration coefficient so as to make the measured value as displayed conform to the mass of the loaded weight. Such calibration is preferably conducted by the user of a balance not only when the balance is set but also as occasions demand or periodically so as to compensate for a span drift or other changes caused by the change of the component parts of a balance that occurs as time passes.
To make the above operation of calibration easy, there has been proposed an electronic balance which has a built-in calibration weight within its housing so as to enable calibration without the necessity of providing a separate precision calibration weight. To have a built-in calibration weight, the housing of a balance must have a large space to accommodate the calibration weight and a mechanism for loading and unloading the weight on and from the weighing means. The mechanism, however, is complicated in contruction and expensive, thereby increasing the cost of the balance. A balance of a large weighing capacity would require a large calibration weight having a large volume, so that it would be practically difficult to provide in the housing a space sufficient for the calibration weight and the associated mechanism.
There has also been proposed a method for calibrating a balance of a large weighing capacity with a calibration weight of a small mass. This method, however, necessarily involves changes in the lever ratio by shocks in transporting the balance or the atmospheric temperature, with resulting deterioration of the accuracy of calibration.